A physical network based on Wavelength Division Multiplexing (WDM), which consists of wavelength paths and OXCs (optical cross-connects), provides wavelength paths connecting nodes in an upper layer to construct a virtual network topology (virtual network) by using wavelength-routing capabilities, thereby providing a flexible communication network infrastructure for realizing various services. As wavelengths for the physical network are bottleneck resources, they have to be utilized effectively. Therefore, to accommodate traffic on a wavelength-routed network effectively, there have been attempted a number of researches about virtual network controls for constructing a virtual network in response to traffic appropriately (see non-patent documents Nos. 1 and 2).
A virtual network is a logical network of an upper layer accommodated on a wavelength network. If the upper layer is an IP, the virtual network topology corresponds to a construction of logical connections. A communication infrastructure installation in itself belongs to a physical network. A virtual network is built up by dividing resources of this physical network logically and allocating a part of the resources to the virtual network. In general, a physical network has a capability of accommodating one or more virtual networks.
For a given traffic demand matrix, non-patent document Nos. 1 and 2 propose an optimization-based method and a heuristic method for designing an optimum virtual network to accommodate its traffic. A traffic demand matrix is a matrix representing a traffic demand between any two nodes in a network, thereby expressing a cross traffic of the whole network.
Recent developments in internet technology bring new services as typified by P2P network, VoIP and video-on-demand into sight, thereby increasingly changing the environment on a network. As an example, it has been shown that a network state, such as traffic demand, changes greatly and randomly due to an interaction between overlay networks and traffic engineering. For this reason, it is important to realize a virtual network control adaptable to an unexpected change in traffic demand.
To adopt to change in traffic demand and accommodate a traffic on a virtual network effectively, there is proposed an approach (on-line control) of dynamically reconstructing a virtual network, based on periodical measuring of a network and periodical detecting of deteriorations in performance of a virtual network (see non-patent document No. 3). Different from off-line control, since such an on-line control allows the virtual network to be reconstructed in response to a fluctuating traffic, it is possible to cope with fluctuations in traffic demand.